1. Field of the Invention
The present invention relates to an arteriosclerosis evaluating apparatus that evaluates a degree of arteriosclerosis of a living being, based on a form of a cuff pulse wave obtained from the being.
2. Related Art Statement
It is known that the form of a pulse wave produced from an artery changes as the artery hardens. Hence, there is known a method of evaluating a degree of arteriosclerosis of a patient by judging which one of predetermined types of waveform patterns corresponding to different degrees of arteriosclerosis the form of an arterial pulse wave detected from the patient is classified as. For example, there is known a method of classifying a detected pulse wave as one of four types, based on a percussion wave and a tidal wave of the pulse wave (e.g., cf. Non-Patent Document 1 (Yoshiaki Masuda, Hiroshi Kanai “Fundamental and Clinical Study of Arterial Pulse Wave”, 1st Edition, p.28–31, Kyoritsu Shuppan K. K., March 2000)). The four types include Type I characterized in that the percussion wave is higher than the tidal wave; Type II characterized in the tidal wave is higher than the percussion wave and a clear local minimum point is present between the two waves; Type III characterized in that the two waves are incompletely fused with each other; and Type IV characterized in that the two waves are completely fused with each other. Type I is the lowest degree of arteriosclerosis, the possibility of advancement of arteriosclerosis increases as the number increases, and Type IV is the evaluation of the highest degree of arteriosclerosis. FIG. 2 shows respective typical waveform patterns corresponding to Types I, II, III, and IV. In FIG. 2, p-wave indicates a percussion wave; and t-wave indicates a tidal wave.
There is also known a method of classifying a pulse wave as one of three types, based on respective peaks of a percussion wave and a tidal wave of the pulse wave (e.g., cf. Non-Patent Document 2 (Joseph P. Murgo, Nico Westerhof, John P. Giolma, Stephen A. Altobelli, “Aortic Input Impedance in Normal Man: Relationship to Pressure Wave Forms”, Circulation, Vol. 62, No. 1, p105–116, July 1980)). The three types include Type A characterized in that the peak of the percussion wave is higher than that of the tidal wave; Type B characterized in the respective peaks of the percussion wave and the tidal wave are level with each other; and Type C characterized in that the peak of the tidal wave is higher than that of the percussion wave.
Meanwhile, blood-pressure measuring devices each employing a cuff are widely used. Hence, there have been proposed various devices that obtain, from a cuff pulse wave detected from the cuff, other sorts of physical information than blood pressure. For example, Patent Document 1 (i.e., Japanese Patent Document No. 2001-346769 or its corresponding U.S. Pat. No. 6,491,638) discloses a device that determines a pulse period, i.e., a pulse rate from a time interval between respective periodic points, such as rising points or peak points, of successive heartbeat-synchronous pulses of a cuff pulse wave. The cuff pulse wave is detected from a cuff in a state in which a pressure in the cuff is lower than a diastolic blood pressure of a living subject, because it has been speculated that if the pressure of the cuff is higher than the diastolic blood pressure, then the cuff pulse wave detected is distorted and accordingly does not have an accurate form.
In the above-described method in which arteriosclerosis is evaluated based on the form of a pulse wave, a cuff pulse wave may be used as it is used in the device disclosed by Patent Document 1. However, it has been elucidated that a cuff pulse wave detected in the state in which the pressure of a cuff is lower than a diastolic blood pressure of a living subject, has a problem that a high-frequency component of the cuff pulse wave is not clear. Since the high-frequency component of the cuff pulse wave includes the above-mentioned percussion and tidal waves, i.e., those portions that change as the degree of arteriosclerosis changes, a degree of arteriosclerosis evaluated based on the form of the cuff pulse wave detected in the state in which the pressure of the cuff is lower than the diastolic blood pressure of the subject, cannot enjoy a sufficiently high accuracy.